Two Independent TDs have told Minister for Finance Michael Noonan they will consider going to the High Court to stop him reaching final agreement on the restructuring of the promissory notes without the approval of the Dáil.

In letters to Mr Noonan earlier this month, Shane Ross and Stephen Donnelly asked the minister to give a commitment that any agreement will be put before the Dáil for approval.

In the absence of such approval, the TDs said they would consider legal action to seek an injunction.

The letters were handed in to the High Court on the final day of a challenge by Dublin businessman David Hall to the legality of the promissory notes used to refinance Anglo and other banks in amounts totalling €31bn.

Mr Ross, Mr Donnelly and People Before Profit TD Joan Collins came to court to show support for the legal challenge against the use of promissory notes.

Their solicitor, Tony Williams, told the court they had a long history of public comment on the notes.

They were not neutral, they had written letters to the Minister for Finance and had been told to stand back and wait for the issues to be dealt with in the court case.

Mr Williams said the TDs were not asking to join the case but they were supportive of it.

He said it would be a shame if questions were raised about Mr Hall's right to take the case as a citizen.

The move followed submissions by counsel for the State that Mr Hall had no legal standing to take the case.

Michael McDowell said Mr Hall was complaining that Dáil powers had been impugned yet no TD had taken any action.

He said the TDs' presence in court and the letters did not change anything, in fact it strengthened his case. He said they knew about the case but chose not to join it, despite threatening other legal proceedings.

Mr Hall is challenging the legality of the promissory notes and their duration.

He says a Dáil vote should have been taken and he wants the court to declare them invalid under the constitution.

After a four-day hearing, Mr Justice Nicholas Kearns said he had a lot to think about and he would deliver judgment at a later date.

In the letters handed into court Mr Donnelly and Mr Ross said it appeared the negotiations on a restructure of the promissory notes provided under the Credit Institutions Act were advanced and expected to conclude before the end of March.

They said public funds could not be appropriated without the prior approval of the Dáil and refer to Mr Hall's challenge in the High Court.

The letter adds: "We call upon you to confirm no such binding agreement will be entered into by you on behalf of the State, absent the approval of the members of Dáil Éireann. In the event that you do not provide such a commitment before 15 January we intend to seek relief in the courts."

A reply from the minister said the ongoing case by Mr Hall had "a constraining effect" on his reply.

However, the minister said if any approval of Dáil Éireann was to be required it would be sought at the appropriate time and an assessment of that issue could best be made "when the shape of a final agreement was fully apparent and finalised".

Mr Ross and Mr Donnelly said they were prepared to accept an undertaking to make the terms of any agreement known to the Dáil and so that members could consider if Dáil approval was required and to allow them time to bring the matter before the courts if necessary.